1. Field of the Invention
This invention relates generally to a process and composition for removing Lewis acid and oxidant impurities from arsine, phosphine, ammonia, and inert gases.
2. Description of the Related Art
Arsine, phosphine, and ammonia are widely used in the semiconductor industry for the manufacture of microcircuitry devices, as source reagents for elemental arsenic, phosphorus, and nitrogen, respectively.
In such applications, it is critical that the arsine, phosphine, and ammonia source reagents be essentially completely free of impurities such as water and oxygen. Such impurities, when introduced onto the semiconductor chip during its manufacture, tend to produce localized defects in the crystalline structure which may then propagate to produce an undesirable epitaxy, and render the chip deficient or even useless for its intended purpose.
Arsine and phosphine are particularly difficult to purify, due to their extreme toxicity and hazardous character, and the fact that they react detrimentally with many otherwise potentially useful scavengers to poison to active sorption sites of such materials. In addition, arsine and phosphine have a higher affinity for water than they do for inert impurities, e.g., nitrogen, which are less objectionable in the semiconductor manufacturing process.
Although ammonia does not possess the toxicity and handling disadvantages of arsine and phosphine, it nonetheless is a poison to many otherwise potentially useful scavengers, such as those commonly used in redox purification systems for removal of water and oxygen contaminants from other gases.
Among the methods utilized in the prior art for removing water from ammonia are the use of moisture-sorptive molecular sieves. The difficulty of employing such method for production of high-purity ammonia for semiconductor applications is that ammonia is competitive with water for the adsorption sites on the molecular sieves. As a result, it is not possible to obtain the necessary low residual water values, on the order of part-per-million concentration of water in the effluent from the molecular sieve contacting step.
Ammonia has also been dehydrated by sodium metal followed by distillation, although such methods are complex, costly, and entail the use of strong reducing agents.
Arsine and phosphine have also been treated by molecular sieves to remove water, but such treatment in order to achieve high water removal efficiency requires that the molecular sieve contacting be carried out at low temperatures, e.g., on the order of about -20 degrees Centigrade for arsine. This and other refrigeration-based water removal techniques involve high energy expenditures and operating costs, and therefore are not fully satisfactory.
In addition, trimetal eutectics comprising indium and gallium components, and liquid at room temperatures, have been employed for purifying arsine and phosphine of water impurity, but such dehydration method suffers the disadvantage that substantial amounts of oxide particles are generated in the treatment stream.
Apart from arsine, phosphine, and ammonia, a variety of inert gases are employed in semiconductor manufacturing, for which extremely high purity is also required. As used herein, the term "inert gases" is intended to be broadly construed as being inclusive of gases which may be unreactive in various semiconductor manufacturing operations, and are selected from the group consisting of one or more members of the group consisting of nitrogen, hydrogen, helium, argon, neon, xenon, silane, germane, and gaseous hydrocarbons (methane, ethane, ethylene, propane, propylene, etc.).
Japanese Kokai Tokkyo Koho No. JP 60/222127 discloses the thermal decomposition of trimethyl aluminum to deposit elemental aluminum on a glass substrate, e.g., glass beads, following which the aluminum coating is reacted with arsine to form a scavenger for water and oxygen.
U.S. Pat. No. 4,603,148 to G. M. Tom discloses a macroreticulate polymer scavenger for removing Lewis acid and oxidant impurities from inert fluids such as aliphatic hydrocarbons, olefins, and gases including nitrogen, argon, helium, xenon, hydrogen, carbon tetrafluoride, ammonia, and silane. The macroreticulate polymer backbone of the scavenger has bonded thereto a plurality of functional groups of the formula: ##STR1## where: Ar is an aromatic hydrocarbon radical of 1-3 rings; R.sub.1 and R.sub.2 are each independently hydrogen, C.sub.1 -C.sub.12 alkyl, methylene-bridged benzophenone, methylene-bridged fluorenone, or alkali or alkaline earth metal salts of such benzophenone or fluorenone radicals; and M is lithium, potassium, sodium, alkyl magnesium, or alkyl zinc, the alkyl substituents being C.sub.1 -C.sub.12 alkyl. Within the pores of the macroreticulate polymer is a metallating agent selected from the group consisting of alkyl lithium, alkyl sodium, alkyl potassium, dialkyl magnesium, alkyl magnesium halide, dialkyl zinc, wherein the alkyl moiety is C.sub.1 -C.sub.12 alkyl; alkali or alkaline earth metal salts of benzophenone; and alkali or alkaline earth metal salts of fluorenone.
It is an object of the present invention to provide a highly efficient composition and process for removing Lewis acid and oxidant impurities from arsine, phosphine, ammonia, and inert gases.
It is another object of the invention to provide a composition and process of such type, which when employed to dry arsine, phosphine, ammonia, and inert gas streams, is capable of reducing the water content of the treated stream to levels on the order of 0.01 part per million by volume and less.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.